The present invention relates to cathodoluminescent flat image display devices.
Recently flat image display devices have been suggested having a viewing screen of about 75.times.100 cm. and a total depth of about 2.5 to 10.0 cm. One such device is described in U.S. patent application No. 607,492 now U.S. Pat. No. 4,031,427 entitled "Flat Electron Beam Addressed Device" filed on Aug. 25, 1975 by T. O. Stanley. This type of device utilizes a plurality of electron beams which excite different portions of a large phosphor screen. A plurality of electron beam guides extend between the front and rear surfaces of the device to direct the electron beams to the proper area of the screen.
If such devices are to be utilized for the display of television information, a high degree of brightness uniformity must exist across the entire viewing surface. This high degree of brightness uniformity is difficult to achieve in devices employing a plurality of electron beams to scan different portions of the display. Since the electron current of each beam may not be equal, the various portions of the phosphor screen may not be excited equally.
This problem of non-uniformity has not existed in conventional cathode ray tubes since a single electron beam scans all of the picture elements or in the case of a color tube all of the picture elements of one color. Therefore, each picture element receives a controlled amount of excitation energy. However, in large area flat cathodoluminescent display devices, the internal support necessary to prevent the collapse of the evacuated envelope under atmospheric pressure makes it difficult to conventionally scan the entire viewing surface with a single beam.